Handedness on Tristan da Cunha: The Genetic Consequences of Social Isolation

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Provins (1990) has suggested that the apparently low incidence of left‐handedness on the island of Tristan da Cunha is the result of social pressures such as deference to authority and group conformity, and that “any genetic factor determining left‐handedness must be very weak”. Here we use a large number of Monte Carlo simulations (n = 10,825) of the growth of the population of Tristan da Cunha from 1827 to 1961, to show that if the original population was randomly selected from a large population with a typical gene‐frequency, then a combination of founder effects, genetic drift and evolutionary bottlenecks can readily explain the fairly low incidence of left‐handedness that was found. Indeed in 15% of the simulations the c‐allele, which is postulated to be responsible for left‐handedness, has disappeared entirely, resulting in a population with no left‐handers at all. The data from Tristan da Cunha are therefore entirely compatible with a genetic model of left‐handedness.